Winter White

You may have noticed the advent of winter in more than just a change in ambient temperature. There are fewer leaves, fewer bugs, and fewer birds. The surfaces we tread upon outdoors change in texture and normally turn a lighter color. Indeed, most of us get paler, too, and heavier, encumbered with thicker trappings.

Many other animals also put on heavier coats. A few actually pale all the way to white. I regret we don’t live with arctic foxes, tundra hares or the willow ptarmigan. But we do cohabit with snowshoe hares, ermines and long-tailed weasels. These three also completely change their seasonal garb from shades of brown and gray to snow white and then back again in spring.

It doesn’t take much effort to imagine the advantages of this seasonal fashion change. Ermines, also called short-tailed weasels, and the somewhat larger long-tailed weasels hunt small animals over and under the snow cover. There is a huge benefit in being difficult for your targeted dinner to see you coming and take evasive action. Although mice, voles and shrews might have benefited from adopting similar strategies, their high reproductive rates are adequate for the continued survival of their species.

Another advantage to the weasels’ winter camouflage: weasels themselves are sought by owls, hawks, fishers, foxes, coyotes and bobcats.  Tips of the tails of both of our local weasels remain black both summer and winter. Biologists have a plausible explanation for this seeming paradox: predators are apt to fixate on the more expendable bobbing tail, a far safer target from the weasel’s point of view.

Mink, another smallish member of the Mustelide family, remain chestnut-colored year round. They hunt along and in dark waters for their meals, and a change to a lighter color would prove disastrous for them.

Weasel predators and the weasels themselves all hunt the snowshoe hare. Also known as the varying hare, the snowshoe hare is the only wild Lagamorph we are likely to see in the central and northern parts of New Hampshire. The best strategy for the hare is to remain motionless and hopefully unseen. Unlike the weasels, the snowshoe hare changes only the color of its guard hairs, the longest, coarsest hairs that make up its outer coat. In September or October these start to grow in pure white, obscuring the darker underfur.

Biologists suggest the color white exchanges less heat with the surrounding environment, meaning that although a white coat absorbs less heat from the sun, it also allows less body heat to escape.

For snowshoe hares, the autumn molt starts on the ears, feet, and legs, and ends on the back. In March, the spring molt starts on the forehead, muzzle, and body and finishes with the ears and feet. The mottled effect usually coincides with the mottled effect of patchy snowmelt. Weasels also have definite molt patterns, which follow approximately the same schedule as the hares.
Temperature change isn’t the major factor stimulating color change. Shedding is triggered by day length. The reduced intensity of light entering through an animal’s eyes as the days shorten signals the pituitary gland in the brain to start the fall molt. This gland also regulates the release of pigment to cells in the hair follicles, resulting in a color change. As the days lengthen again, the spring molt reverses the color scheme. Long-tailed weasels and snowshoe hares don’t change color in the snowless parts of their ranges.

Though some of us may yearn for early melts or even snow-free winters, some of the other residents prefer and may even require snowy winter seasons. I wonder how they are faring this year.

By J. Ann Eldridge, Wildlife Coverts Cooperator

2/01/07

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